Influence of NaCl, NaNO2and oxygen on the germination and growth ofBacillus licheniformis, a spoilage organism of chub-packed luncheon meat

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Abstract
The thermal resistance of B. licheniformis spores was increased from a D70-value of 590 min to 1 of 900 min by the addition of 4% NaCl to the heating medium [tryptone-yeast extract-glucose (TYG) broth, pH 6.8], but was decreased to 470 min in YTG broth acidified to pH 4.4. Sodium nitrate (0.02%) enhanced spore destruction at 80.degree. C but not at 70.degree. C; addition of 4% NaCl eliminated this effect. Less than half the number of spores surviving heat comparable to commercial cooking were heat-damaged to the extent of being unable to grow aerobically in the presence of 4% NaCl. No growth occurred during anaerobic incubation even when the media contained no added NaCl. O2 was not required to trigger spore germination, but trace amounts were needed for the successful outgrowth of germinated spores. Spore germination was accelerated and enhanced by the presence of at least 2% NaCl. Under anaerobic conditions NaCl promotes microbiological stability because the germinated spores cannot develop further and become moribund. The plastic casing of luncheon-meat chubs is not sufficiently O2-impermeable to allow the product a long shelf-life other than at chill temperatures unless the chubs are stored in an O2-free atmosphere.